Benzoyl-substituted (η6-arene)tricarbonylchromium complexes: Synthesis and structure

Article abstract of DOI:10.1016/j.jorganchem.2006.10.055

Lithiation of chloro- and methoxy-(η⁶-benzene)tricarbonylchromium complexes yielded, after electrophilic quench with a Weinreb amide, the corresponding benzoyl-substituted complexes. One of them has been investigated by an X-ray diffraction study.

Full text of DOI:10.1016/j.jorganchem.2006.10.055

Journal of Organometallic Chemistry 692 (2007) 1216–1218
www.elsevier.com/locate/jorganchem
Communication
Benzoyl-substituted (g6-arene)tricarbonylchromium
complexes: Synthesis and structure
a
a,
a,
b
Antoine Eloi , Franc¸oise Rose-Munch *, Eric Rose *, Patrick Herson
a
Universite´ Pierre et Marie Curie-Paris6, Laboratoire de Chimie Organique (UMR CNRS 7611), Institut de Chimie Mole´culaire
(FR 2769), Case 181, 4 place Jussieu, F-75252 Paris Cedex 05, France
b
Universite´ Pierre et Marie Curie-Paris6, Laboratoire de Chimie Inorganique et Mate´riaux, Mole´culaires (UMR 7071),
Case 42, 4 place Jussieu, F-75252 Paris Cedex 05, France
Received 29 September 2006; received in revised form 24 October 2006; accepted 24 October 2006
Available online 3 November 2006
Dedicated to Stefano Maiorana on the occasion of his 70th birthday.
Abstract
Lithiation of chloro- and methoxy-(g6-benzene)tricarbonylchromium complexes yielded, after electrophilic quench with a Weinreb
amide, the corresponding benzoyl-substituted complexes. One of them has been investigated by an X-ray diffraction study.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Chromium; (Arenetricarbonyl) complexes; Weinreb amide; Lithiation
1. Introduction
of electrophiles have been reported for the anion trapping
step. Among them, electrophilic halide sources, alkylating
agents, heteroatom nucleophiles were widely used. Car-
bonyl compounds including aldehydes, acid chlorides,
anhydrides, esters, amides, ketones were reported to react
with lithiated (arene)Cr(CO)3 complexes [5c].
In the course of our research into the functionalization
of organochromium complexes we were interested in the
preparation of such complexes substituted by a keto group
[6,7]. This communication describes the easy syntheses of
benzoyl-substituted (g6-arene tricarbonylchromium) com-
plexes by lithiation/electrophilic quench sequence using a
Weinreb amide as the electrophile.
The coordination of an arene to metal carbonyl moieties
[M(CO)3] strongly modifies the reactivity of the arene
ligand. In particular, the arene complexes of chromium have
been the subject of extensive development due to their sig-
nificant applications in organic synthesis [1]. Furthermore,
an expanding area of the use of metal carbonyls has been
developed in bioorganometallic chemistry, increasing the
potential of Cr complexes in such a field [2,3].
In the course of our research into organochromium and
organomanganese complexes [4] we were interested in one
of the major changings of the coordinated arene: the acid-
ification of the hydrogens attached to the aromatic ring
which strongly facilitates the direct proton abstraction fol-
lowed by electrophilic trapping. This reaction has been
extensively explored in (arene)Cr(CO)3 complexes and
has been the subject of several reviews [5]. Different types
2. Results and discussion
The reaction of the anions of complexes 1a,b, obtained
by addition at low temperature of n-BuLi to the correspond-
ing complexes, with the Weinreb amide 2 [8] led to the for-
mation of two new complexes substituted by a benzoyl
group: 3a in 43% yield and 3b in 46% yield (Scheme 1). This
reaction is highly regioselective: only the ortho-substituted
*
Corresponding authors. Tel.: +33 144276235; fax: +33 144275504
(E. Rose).
E-mail address: rose@ccr.jussieu.fr (F. Rose-Munch).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.10.055

A. Eloi et al. / Journal of Organometallic Chemistry 692 (2007) 1216–1218
1217
Li
n-BuLi
R
R
Cr(CO)
Cr(CO)
O
3
3
1a R = Cl
1b R = OMe
Ph
COPh
R
NMe(OMe)
2
3a R = Cl
3b R = OMe
Cr(CO)
3
Scheme 1.
compounds were isolated. Although the yields were not
entirely satisfying, this reaction represents a significant
improvement in the synthesis of such complexes. Indeed,
the preparation of 3a or 3b by direct coordination of the cor-
responding free ligands to Cr(CO)3 resulted in the forma-
tion of three compounds difficult to purify by silica gel
chromatography column: two complexes (4 and 5), where
the chromium entity Cr(CO)3 coordinated the substituted
or the unsubstituted arene ring, and the last one (6), a bime-
tallic compound, where the chromium entity coordinated
the two arene rings at the same time [9] (Scheme 2).
Several years ago [6], we achieved the synthesis of g6-(2-
thiophenyl) carbonylarenetricarbonylchromium complexes
using palladium-catalyzed process under a carbon monox-
ide atmosphere and a judicious choice of reaction condi-
tions. But this methodology needs the presence of an
halogen substituent on the arene ring of the starting mate-
rial to allow the insertion of the palladium active species
into the C–halogen bond, thus limiting the choice of the
starting complexes.
˚
Fig. 1. Two views of the ORTEP diagram of 3a. Selected bond lengths (A)
and angles (ꢁ): Cr–C1, 2.216(2); Cr–C2, 2.230(2); Cr–C3, 2.204(2); Cr–C4,
2.229(2); Cr–C5, 2.219(2); Cr–C6, 2.222(2); Cr–O, 1.225(3); C2–C7,
1.525(3); C7–C8, 1.492(3).
1H NMR spectra of complexes 3a and 3b exhibit well
resolved doublets and triplets for the H3–H6 protons. As
expected, the conformations in solution of the major iso-
mers of both complexes are anti-eclipsed with respect with
the keto group [10]. For the anisole derivative 3b, there is a
synergic effect between the methoxy and the keto groups.
Indeed, the electron-donating methoxy group favours a
conformation which eclipses this substituent and the elec-
tronwithdrawing benzoyl group favours a conformation
which anti-eclipses the carbonyl residue. Thus, the differ-
ence of chemical shifts between the H4 and H5 protons is
larger in 3b: 0.74 ppm than in 3a: 0.62 ppm.
We obtained some monocrystals of complex 3a and sub-
jected them to X-ray analysis. Two views of ORTEP dia-
gram as well as selected bond lengths are reported Fig. 1.
The torsion angles C1–C100–Cr–C15, C5–C100–Cr–C16,
and C3–C100–Cr–C14 are 21.45ꢁ, 19.80ꢁ, and 20.61ꢁ,
respectively (C100 being the center of the six-membered
ring). The free arene plane is not parallel to the coordinated
arene plane, with a dihedral angle value of 68ꢁ. The
carbonyl function, which lies almost in the plane of the
uncoordinated arene ring, is pointing out in the direction
of the Cr(CO)3 entity with a dihedral angle of 46ꢁ with
the coordinated cycle. It is interesting to note that, in the
case of the [g6-(2-thiophenyl)carbonyl-p-methoxybenzene]-
tricarbonylchromium complex [6], the carbonyl function
was found to point in the direction opposite to the Cr(CO)3
moiety with a dihedral angle of 14ꢁ with the six-membered
arene ring.
R
COPh
Cr(CO)
R
4
5
3
R
Cr(CO)
6
CO
COPh
(CO) Cr
3
R
CO
6
Cr(CO)
(CO) Cr
3
3
Scheme 2.

1218
A. Eloi et al. / Journal of Organometallic Chemistry 692 (2007) 1216–1218
˚
3. Conclusion
Z = 4, k(M0-Ka) = 0.71073 A, nb of data collected =
12896, nb of unique data collected = 4219, nb of unique data
used for refinement 2162(Fo)2 > 3r(Fo)2, R(F) = 0.0312,
Rw(F2) = 0.0344.
These results address the potentiality of the Weinreb
amide 2 in the preparation of benzoyl-substituted (g6-
arene)tricarbonylchromium complexes. This electrophile
allows the easy formation of such complexes after a lithia-
tion/electrophilic quench sequence of halogeno- and meth-
oxy-substituted (arene)Cr(CO)3 complexes. Work is in
progress in order to generalize these results to other
diversely substituted complexes.
5. Supplementary material
CCDC 622365 contains the supplementary crystallo-
graphic data for 3a. The data can be obtained free of charge
via htpp://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
4. Experimental
All chemicals were used as supplied, unless noted other-
wise. All NMR spectra were obtained on a Bruker 250 or
400 in CDCl3 and are referenced to external TMS. Elemen-
tal analyses were performed by the ‘‘Service de microanal-
yses de l’UPMC’’.
Acknowledgments
The authors thank CNRS for financial support and
Prof. C. Rolando and Dr. G. Ricart from the ‘‘Universite
´
des Sciences et Techniques’’ de Lille (France) for MS
analyses.
4.1. Typical procedure: preparation of complex 3a
Chlorobenzenetricarbonylchromium 1a (321 mg, 1.29
mmol) in THF (10 mL) was stirred at À78 ꢁC in a flask
under dry nitrogen. n-BuLi (0.72 mL, 1.8 mmol) was added
to this yellow solution. The solution became pink then
orange. After 90 min, the Weinreb amide PhCON-
(Me)(OMe) 2 (421 mg, 2.55 mmol) was introduced via a
canula at À78ꢁC and the reaction mixture stirred for 2 h.
This solution was introduced at 0 ꢁC into another flask
containing AcOH (11 mL) and water (9 mL) at 0 ꢁC. The
mixture was then extracted twice with Et2O (2 · 30 mL),
with a saturated K2CO3/H2O solution and with a saturated
NaCl/H2O solution. After evaporation of the organic
phase, an orange solid was recovered which was purified
by silica gel chromatography column with a petroleum-
ether/dichloromethane mixture 100/0 until 0/100 ratio.
The orange red solution was evaporated under reduced
pressure and recrystallized: 196 mg, 43% yield of 3a.
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´
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˚
a = 12.203(2), b = 10.447(3), c = 12.760(2) A, a = 90ꢁ,
3
˚
b = 116.761(14)ꢁ, c = 90ꢁ. U = 1452.5(6) A , T = 250 K,